The Production of Extracellular Polysaccharide by the Unicellular Red Algaporphyridium Aerugineum¹,²

SUMMARY The unicellular red alga Porphyridium aerugineum was shown to be encapsulated by an amorphous, water‐soluble, polyanionic polysaccharide of high molecular weight. The encapsulating polysaccharide is qualitatively identical with polysaccharide found dissolved in large quantity in the culture medium. The kinetics of extracellular polysaccharide production as a function of cell age was studied. Rates of production (on a per cell basis) of both encapsulating and dissolved polysaccharides are greatest in stationary phase light‐grown cultures. Dissolved polysaccharide was quantitatively isolated by precipitation with cetyl pyridinium chloride, conversion to the calcium salt, and reprecipitation with ethanol. The procedure yields a spectrally pure product, which is composed of glucose, galactose, xylose, and 2 undetermined, sugar components, and has a sulfate content of 7.6% by weight. Electron microscopy of Porphyridium revealed that Golgi vesicles transport, polymerized polysaccharides to and through the cell membrane. Similar vesicles were observed in the multicellular Pseudogloiophloea , indicating that the Golgi complex plays a crucial role in the production of extracellular polysaccharides by the red algae. H 14 CO 3 ‐ pulse‐label experiments resulted in labeled extracellular polysaccharide in which all the constituent components contained 14 C. Rates of excretion of polysaccharide were found, to follow a cyclic pattern, correlated generally with the division cycle, of the cell.